Levothyroxine and Furosemide: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Furosemide
Levothyroxine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased risk of free thyroid hormones, followed by an overall decrease in total thyroid hormone levels
Interaction Deep Dive
Concomitant use of furosemide (greater than 80 mg) with thyroid hormones may inhibit the binding of thyroid hormones to carrier proteins resulting in transient increase in free thyroid hormones, followed by an overall decrease in total thyroid hormone levels. Monitor the total thyroid hormone levels when used concomitantly with furosemide1.
Why it happens (mechanism)
Inhibition of binding thyroid hormone carrier proteins
Common questions
Can I take Levothyroxine and Furosemide together?
Increased risk of free thyroid hormones, followed by an overall decrease in total thyroid hormone levels Always confirm with your pharmacist or prescriber before making any change.
How serious is the Levothyroxine and Furosemide interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Levothyroxine or Furosemide need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (1)
- Product Information: FUROSCIX(R) subcutaneous injection, furosemide subcutaneous injection. scPharmaceuticals Inc (per FDA), Burlington, MA, 2022. DailyMed
Keep reading about Furosemide
Keep reading about Levothyroxine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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